The flexible plastic bag is one of the most ubiquitous commodities in commercial usage today. There are many different designs and methods for manufacturing these bags. The plastic bags of the present invention have integral, sinusoidally-shaped ties cut into the plastic bag body. Bags of the type described in the present invention are shown in U.S. Pat. No. 4,890,736, issued to Greyvenstein on Jan. 2, 1990.
Current plastic bag manufacture involves utilizing thinner plastic materials that are folded and stacked at ever increasing speeds. Thinner plastic reduces the landfill space. In addition, more of the thinner bags can be packaged in a given container, or, conversely, a smaller package can accommodate the same number of thinner bags.
Thinner bags, however, increase manufacturing problems. Most particularly affected are the folding and stacking operations.
As production speed increases, the registration of the bags becomes more difficult. There is less tolerance in the proper location of a bag disposed in the speeding web as it is introduced to a sizing, folding or stacking operation. A criticality develops as the product is transferred from one feed mechanism to another in the chain of manufacturing operations. Hence, it becomes imperative to provide more direct and positive feed systems, so that the bag bodies will not wrinkle, ripple, jam, flap or cause interruptions in the manufacturing operations.
The registration of a bag as it is separated from the continuous web of material can no longer be treated as one in a series of items to be handled. Rather, the high speed necessitates that registration sensing must take place in advance of the actual cutting and sizing of the bags. The present invention reflects the discovery that such forward registration techniques must use a "floating" average of several bag locations as they are sensed upstream. The averaging of a plurality of bag location signals provides a trend adjustment for registration that is suitable (i.e., within tolerance) for the high-speed cutting operation, utilizing the center line for each bag being introduced to the sizing and cutting apparatus downstream.